落地 12.2 二十个用例目录：toml + .st + 期望表。

- tests/cases/ 01~20：13 正例 / 6 负例 / 1 运行时故障
- 负例冻结报错类别：非 GVL 写全局、同名全局、io.var 未声明、FUNCTION 写全局、未声明实例、循环调用
- tests/README 补充用例清单与点亮节奏

tests/cases/16_fb_undeclared/EXPECTED.md

@@ -0,0 +1,4 @@
+# 期望：编译错误
+
+- 调用 `starter(...)` 但未声明实例
+- 报错类别：FB 必须先声明实例才能调用

tests/cases/16_fb_undeclared/main.st

@@ -0,0 +1,7 @@
+PROGRAM MAIN
+VAR
+    q : BOOL;
+END_VAR
+    starter(start := TRUE, stop := FALSE);
+    q := starter.Q;
+END_PROGRAM

tests/cases/16_fb_undeclared/motor.st

@@ -0,0 +1,9 @@
+FUNCTION_BLOCK MotorStarter
+VAR_INPUT
+    start, stop : BOOL;
+END_VAR
+VAR_OUTPUT
+    Q : BOOL;
+END_VAR
+    Q := start AND NOT stop;
+END_FUNCTION_BLOCK

tests/cases/16_fb_undeclared/project.toml

@@ -0,0 +1,8 @@
+[project]
+name = "case16"
+entry = "program MAIN"
+cycle_limit = 1000
+dt_ms = 10
+
+[files]
+st = ["motor.st", "main.st"]